If you have minimized any window in Windows 7 taskbar; hold the SHIFT key from your keyboard and then click to maximize (normal left click) it. A new window of that opened program (or another instance of that program) will open.
Giving some example will make it more clear.
Suppose, you have kept Internet Explorer minimized in the taskbar. Now, if you hold the SHIFT key and click it to maximize, the minimized Windows of Internet Explorer’s pages (which you minimized) will open PLUS a new window of Internet Explorer will open.
If you have minimized MS Paint and if you hold the SHIFT key and click it to maximize, the minimized My Computer or that folder PLUS a new instance of MS Paint will open.
So, it is a kind of “buy one, get one free” type tutorial or is actually a kind of shortcut to open another window type trick.